1. Field of the Invention
This invention relates to a system adapted to be connected to the electrical system and the accelerator pedal of a conventional vehicle to allow the operator to set and maintain a desired cruising speed without the need for modifying the accelerator position as power demands on the engine vary.
2. Prior Art
A variety of devices have been developed to relieve the driver of an automobile or other vehicle of the need to constantly use the vehicle's accelerator pedal to maintain a desired cruising speed for the vehicle. These devices minimize driver fatigue on long trips, eliminate the possibility of the driver unconsciously exceeding legal speed limits and improve the fuel economy of the vehicle by minimizing fuel wasting accelerations.
One class of such automatic engine control devices is adapted to be factory installed in the vehicle during the vehicle manufacture process and involves fluid or electro-mechanical control mechanisms connected to the engine to sense the engine speed and to modify the engine throttle setting to maintain the speed at a level sensed by the operator. These devices are quite complicated and they are accordingly expensive and somewhat unreliable in their operation. Because of their complexity it is extremely expensive to install this type of speed control system on an existing vehicle. One form of such system is disclosed in U.S. Pat. No. 3,476,204.
The expense in installing these complicated speed regulating systems on an existing vehicle and the high cost of the systems even when factory installed led to the development of a simplified form of control which allowed the vehicle operator to automatically achieve a predetermined throttle setting rather than a predetermined engine speed. The operator would control the engine speed through use of the accelerator pedal until the desired speed was attained and then engage the control to maintain the throttle setting attained at that time. While the vehicle speed would change on a hilly road, during level driving conditions this form of control maintained a relatively constant vehicle speed. A device of this type is disclosed in McMaKen U.S. Pat. No. 3,204,734. The device disclosed in that patent may be easily adapted to an existing vehicle as it employs only a single mechanical connection to the vehicle accelerator pedal and simple connections to the vehicle electric system.
Another form of cruise control has been marketed which employs a voltage derived from the engine ignition system as an indication of the vehicle speed and uses this to control the accelerator position and maintain that speed. In this system the operator controls the vehicle speed through the accelerator pedal until a desired speed is reached. He then turns a potentiometer to a setting which generates a voltage equal to the speed relaed voltage generated by the system at that instant. This adjustment process is relatively complex as the operator must sense increases or decreases in vehicle speed to determine when the potentiometer setting equals the speed related voltage. The speed related voltage in this system is developed by a circuit which integrates a series of variable frequency, variable amplitude, constant width pulses. This arrangement depends for its accuracy upon the constant nature of the ignition pulses. If breaker points deteriorate this voltage changes and accordingly the speed control drifts.